</p>

<p>
Interfaces that are not <a href="#Basic_interfaces">basic</a> may only be used as type
constraints, or as elements of other interfaces used as constraints.
They cannot be the types of values or variables, or components of other,
non-interface types.
</p>

<pre>
var x Float                     // illegal: Float is not a basic interface

var x interface{} = Float(nil)  // illegal

type Floatish struct {